Stud welding method and device



y 1960 T. E. SHOUP ETAL Re. 24,832

STUD WELDING METHOD AND DEVICE Original Filed April 8, 1954 2Sheets-Sheet 1 y 1960 T. E. SHOUP EI'AL Re. 24,832

STUD WELDING METHOD AND DEVICE Original Filed April 8, 1954 2Sheets-Sheet 2 fl P FIG.3

NTOR. 14.

PM 4 w.

United States Patent STUD WELDING lVlETHOD AND DEVICE Thomas E. Shoup,Amherst, Roger W. Sholle, Lorain, and Lorenz John Mowry, Elyria, Ohio,assignors to Gregory Industries Inc., Detroit, Mich., a corporation ofMichigan Original No. 2,814,716, dated Nov. 26, 1957, Ser. No. 421,780,Apr. 8, 1954. Application for reissue July 1, 1959, Ser. No. 824,763

18 Claims. (Cl. 219-98) Matter enclosed in heavy brackets I: appears inthe original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention relates to a new method and apparatus for stud welding.

In the majority of stud welding equipment on the market the stud isconnected to one side fo a source of welding current and a plate towhich the stud is to be welded is connected to the other side of thesource of welding current. In the most popular equipment a solenoid in astud welding gun is connected in series with the stud. As soon aswelding current starts to fiow through the solenoid, the stud and plate,the solenoid retracts the stud from the plate to draw an are between thestud and the plate. This are is initiated by the welding current whichflows through the solenoid. After the are has continued for a definiteperiod of time sufficient to melt the end of the stud and the plate, thesource of welding current is disconnnected and the stud is plunged intothe plate. This apparatus and method has produced excellent results onstuds of various diameters and materials.

In another type of stud welding wherein an arc is drawn between the studand the plate, the stud was also lifted from the plate to establish anarc by a solenoid. However, the solenoid was powered by a circuitentirely independent of the welding circuit. A design of this typerequired very close control of the switches and contactors in bothcircuits to ensure correct timing of operation.

In another type of stud welding a high frequency current superimposed onthe welding current has been used to initiate an are between the studand the plate. This type of equipment does not necessarily need asolenoid since the stud can be positioned at the arc distance from theplate and the high frequency current will span the gap to initiate anarc.

In another of the prior devices a solenoid was used to lift the studfrom the plate to establish an are. In this device a solenoid, the stud,and the plate were connected in series to a source of relatively lowcurrent value. The sole purpose of this low current was to lift the studand strike an arc. The welding current source was then connected to thestud and plate with the welding current also flowing through the arc tomelt the end of the stud and the plate. In this device separate sourcesof current were needed for the welding and for the arc initiatingcurrent. The are initiating current flowed throughout the entireduration of the flow of welding current.

These prior devices which require two sources of current do not lendthemselves to a portable hand tool which can easily be moved from placeto place. Many applications of stud welding are performed from batterypower, rectifiers or motor generator sets, in such places as newconstruction, steel mills, etc. Many times on construction jobs and evenin other locations portable power units must be used for the welding. Ifthe stud Re. 24,832 Reissued May 31, 1960.

See

welding equipment will work on a single source of power, the cost andamount of equipment needed for power is greatly reduced. It is onlynecessary to supply one power source for the present invention.

One of the objects of the invention is to provide a portable studwelding tool which will operate from a single. source of power and whichis adapted to weld many sizes of studs.

Another object of the invention is to provide a stud welding device andmethod which lends itself to a small, compact, lightweight handtoolwhich will accommodate studs of many sizes.

Another object of the invention is to provide a stud welding device inwhich the lifting current is not varied by variations in the weldingcurrent even though both currents are obtained from the same source ofpower.

Another object of the invention is to provide a stud welding hand toolwhich will weld studs from approximately Ms" diameter to over 1 /2"diameter without excessive heating of the hand tool.

Another object of the invention is to provide a method of stud weldingwherein the stud, plate and a lifting coil are connected in series to asource of current followed by the connecting of the source of currentdirectly to the stud and plate to melt the end of the stud andsimultaneously shunt the lifting coil to render it ineffective andfinally plunging the stud into the plate and disconnecting the source ofcurrent.

Another object of the invention is to provide a method of stud weldingwherein the lifting coil is shunted by the connecting of the source ofcurrent to the stud and wherein a holding coil is simultaneouslyenergized to hold the stud at the arc distance from the plate.

Other objects and a fuller understanding of the invention will becomeapparent from the following description and claims when taken inconjunction with the drawings in which:

Figure 1 is a view partly in section illustrating a stud welding handtool and the circuit to operate it;

Figure 2 is a schematic illustration of the invention;

Figure 3 is a schematic illustration of a modification of the invention;and

Figure 4 is a schematic illustration of another modification of theinvention.

Figure l'illustrates a complete set of equipment needed to practice themethod of stud welding as described and claimed herein. In practicingthis invention a welding current source P supplies power for welding astud S to a work plate W. The stud S is held by a stud welding gun Gdesigned as a small hand tool and is connected to the welding currentsource P through a control box B. Complete electrical circuit forwelding is obtained by grounding one side of the Welding current sourceP and the work plate W to which the stud is to be welded. The controlbox B starts to operate to control the electrical circuits and thewelding of the stud by closing a gun button finger switch F mounted inthe handle of the gun G. Details of operation and structure of thevarious parts will be described later.

In using apparatus to carry out the method of stud welding the operatorsimply connects the control box B to the welding current source P andthen connects welding gun G to the control box B. A stud S of a desiredsize and shape is fixed in the gun G and the gun is positioned relativeto the work plate W to place the stud against the work plate. Manuallypressing on the gun button F causes the control box to start the flow ofcurrent to lift the stud from the plate and draw an are between the studand the plate. The control box then causes a heavy wel d ing current toflow through the stud, the arc and the plate in a circuit which willshunt a part of the arc initiating and stud lifting circuit. After theheavy welding current has sufliciently melted the end of the stud, thecontrol box disconnects the welding current source and the gun plungesthe stud into the plate.

WELDING CURRENT SOURCE The welding current source P may be acommercially available battery unit, motor generator set, rectifier set,or any other source of heavy current which will provide sufl'icient'power for melting the end of the stud and the adjacent portion of theWork plate. For small cross section studs, such as A3" or /4" diameterstud, the power source is much lighter than the power source for weldinglarge cross section studs such as a 1%" diameter stud. Inwelding thelarge diameter or cross section studs the power source must be capableof supplying upwards oft 5000 amperes or more of welding current for aperiod of time from one to two seconds.

THE GUN AND SOLENOID The gun G or hand tool used in the studweldingopera tion. is mechanically very similar to that illustrated inPatent No. 2,413,189, issued to T. Nelson,.December 24, 1946; and PatentNo. 2,416,915,. issued to C. S. Evans, March 4, 19 47. The gun includessimilar parts, including a plunger spring schematically illustrated inFigure 2 to those parts illustrated in the previouspatents.

The major change in the present gun from the prior gun is in thesolenoid coils used to lift the stud from the plate during welding. Inthe present gun the solenoid includes a stationary armature 11 and amovable armature 12 mounted within the solenoid coil 13. The solenoidcoil 13 has many turns of fine wire which are incapable of carryingwelding current. The coil 13 is energized by the. control box B throughend leads 14 and 15 and a center lead 16 which is connected between theends of the coil. The end leads 14 and 15 are connected to the controlbox by a control cable 17 mounted in the handle of the gun in such amanner that the end leads 14 and 15 pass through the handle to thesolenoid coil 13. The control cable 17 also carries leads 18 and 19which are connected to the gun button or finger switch F mounted in thehandle for manual starting of the welding cycle.

Since the solenoid coil is: constructed of wire which is incapable ofcarrying the welding current, a welding current cable 20 is fastened tothe guns stud holding. means 21 and passes through the handle forconnection directly to the control box. The center lead. 16 from thesolenoid coil 13 is electrically connected to this. welding cable; 20within the gun or hand tool. Such a connection is perfectly safe sincethe current flowing through the center lead. 16 is. relatively small.

The portion of the coil 13 between leads 14 and 16 is termed the liftingportion and the portion of the coil between leads 16 and 15 is termedthe holding portion. These portions may be wound of the same diameterwire, however, it is more advantageous if the lifting portion of thecoil is wound from Wire which will carry heavier current than theholding portion, even though both are very fine wire. Best operation. isobtained when the magnetic polarity of these two portions are in thesame direction so that the magnetic field established by the holdingcoil will be in the same direction as the field originally establishedby the lifting coil. When these fields are in the same direction, thereis no apparent momentary field collapse in the solenoid at the instantthe lifting coil is shunted out and the holding coil is simultaneouslyener- A particular eflfect is noted when the magnetic field establishedby the holding coil is reversed to that established by the lifting coil.Namely, simultaneous energization of the holding coil andde-energization of the lifting coil causes a momentary complete collapseand reversal of the magnetic field. This effects the maintaining of anarc gap between the stud andthe plate. This momentary collapse andreversing of the magnetic field allows the plunger spring 22 to startthe stud towards the plate. If the stud starts towards the plate and theholding coil is not sufiicient-ly strong to re-lift it, the stud willcontinue to plunge into the plate. Thus, if this feature is notdefinitely desired, it is necessary to keep the magnetic fieldsestablished by the lifting and holding coil in aligned polarity so thatthe holding coil will keep the stud retracted from the plate after thelifting coil has been deenergized.

CONTROL BOX The control box B may be constructed of any suitablematerial in the form of a housing which will contain the electricalcircuit control equipment. Such a box must be rugged to withstand abuseobtained through normal usage of the equipment in steel mills,construction jobs, railroads, shipbuilding, etc. The control circuitillustrated in Figure l is identical to the schematic illustration ofFigure 2. In Figure 2 the gun. is illustrated schematically as.containing a solenoid coil, an armature, stud holder and the studplunger spring 22. The stud lifting coil is capable of overcoming thestud plunger spring to lift the stud' from the work plate W. When thecoil is de-energized, the plunger spring 22 plunges the stud into thework plate W. I

The electrical circuits contained in the control box in clude acontactor C1 operated by a contactor coil C, a time delay relay switchTR operated by a time delay coil TD and control relay switches CR1, CR2and CR3 controlled by a control relay coil CR. One end of the coil 13 isconnected by the end lead 14 to one side of the control relay switchCR1. The other side of the control relay switch CR1 is connected by alead 30 to one side 31 of the welding current source P. The other end ofthe coil 13 is connected through end lead 15 to the other side 32 of thewelding current source. As was previously described, the lead 16 fromthe coil 13 is connected to the welding cable 20 within the gun handle.The welding current 20 is connected to one side of the contactor C1located Within the control box and the other side of the contactor C1 isconnected to one side 31 of the welding current source by suitablewelding current lead cable 33. The lead 18 from the gun button F is alsoconnected to the side 31 of the welding. current source and the lead 19from the other side of the gun button is connected to one side of thetime delay relay switch TR. A lead 34 connects the other side of thetime delay relay switch TR to one side of the control relay coil CR andlead 35 connects the other side of the control relay coil CR to the side32 of the welding current source. One side of the control interlockrelay switch CR2 is connected to side 31 by lead 36 and the other sideof this switch CR2 is connected to the time delay coil TD by lead 37.The time delay coil TD is also connected to the side 32- by the lead 38.As is illustrated in Figure 2, the leads 19 and 37 are electricallyjoined. The control relay contactor switch CR3 has one side thereofconnected by lead 39 to side 31 of power source P and the other sidethereof connected by lead 40 to one side of the contactor coil C, theother side of which is connected to side 32 of the welding currentsource by a lead 41.

The welding circuit and control circuits operate as follows: After astud. is placed in the gun and the gun positioned against the work plateW, the operator presses gun button F to electrically connect leads 18and 19. This starts a relatively low value current flowing through leadsI8; 19 and 37,, time delay coil TD and lead 38 to energize the timedelay coil TD. Current also flows through leads 18, '19, 34 and 35 andnormally closed time delay relay switch TR to energize the control relaycoil CR. Energization of control relay coil CR causes it to closeswitches CR1,. CR2 and CR3. The closing of the switch CR2 shunts out thegun button and leads 18 and 19 with current. flowing. through lead 36 tomaintain energization ofcontrol. relay coil. CR and time delay coil TDin case the gun buttonlis released during the welding cycle. The

closing of switch CR1 causes current to flow from the welding currentsource through lead 31, lead 30 and lead 14 through the lift portion ofthe coil 13, through lead 16, welding cable 20, stud holder 21, stud S,work plate W to lead 32 on the other side of the welding current source.This relatively low current flow is suflicient to cause the coil 13 tolift the stud S from the plate W and strike an are between the stud andplate.

The control relay contactor switch CR3 is closed substantiallysimultaneously with switch CR1, and current flow is established frompower source side 31 to side 32 through leads 39 and 40, contactor C andlead 41'at the same time the lifting coil is energized to strike thearc. As soon as coil C is energized, it closes contactor 01 allowingwelding current to flow from power source side 31 through welding cable33, welding cable 20, stud holder 21, stud S and work plate W to side 32of the welding current source. Closing of contactor C1 completely shuntscontrol relay switch CR'1, the lifting portion of the coil 13 and leads14 and 30 rendering the lifting coil ineffective. The holding portion ofthe coil 13 is connected simultaneously in parallel with the are by theleads 16 and to energize this portion of the coil to hold the stud awayfrom the plate for maintaining the arc.

After a predetermined duration of time, the time delay relay switch TRopens, thus de-energizing control relay coil CR. De-energizing controlrelay coil CR opens switches CR1, CR2 and CR3. Opening the switch CR3de-energizes contactor coil C which in turn opens the contactor C1.Opening of contactor C1 stops the flow of welding current through thestud and also stops the flow of very light current through the holdingportion of coil 13 allowing plunging spring 22 to plunge the stud intothe work plate. All of the switches and parts of the circuit and controlbox are now in their original position so that another stud can beplaced in the gun for welding to the work plate at another position.

When the circuit of Figure 2 is used, the plunging spring 22 is held incompressed position and does not start the stud towards the plate untilafter contactor C1 has stopped the flow of welding current, therebyde-energizing the holding coil and the welding arc.

A variation of this method results from using the circuit of Figure 3which is identical to that of Figure 2. except that end lead 15 has beeneliminated. Pressing the finger button F initiates the welding arc andlifts the stud from the work plate in the same manner as has beenpreviously described. However, as soon as the contactor C1 closes toshunt the lifting portion of the solenoid coil, plunger spring 22immediately starts to plunge stud S towards the work plate W. The studstarts to plunge, at the same time full welding current is establishedacross the are between the stud and the work plate. When the time dclayswitch TD is set for a period of time longer than the required time forplunger spring 22 to move the stud S into the work plate W, the weldingarc is snufied out and welding current continues to flow through thestud and plate after they have come into contact. This feature isparticularly useful in those instances where it is advisable to plungethe stud during the flow of welding current and where the stud is liftedfrom the plate only long enough to establish an arc therebetween.

In the circuit of Figure 4 a control relay switch CR4 has been insertedin the solenoid co-il lead 15. This switch CR4 is opened and closed withswitches CR1, CR2 and CR3 by control relay coil CR. The variation in themethod takes place after welding current starts to flow since theremainder -of the circuit is identical with that of Figure 2. In thiscircuit after welding current has been flowing for a predetermined timedinterval established by time delay relay switch TR, the switch TR opensto de-e-nergize relay coil CR. De-energizing of relay coil CR opensswitches CR1, CR2, CR3 and CR4. Opening of switch CR4 de-energizes theholding portion of the solenoid coil 13 and allows the plunger spring 22to start plunging the stud S into the work plate W. Opening of theswitch CR3 dc-energizes contactor coil C to open contactor C1 and stopthe flow of welding current. The time duration between the opening ofswitch CR4 and contactor C1 is dependent on the speed of operation ofcontactor coil C and contactor C1. When this contactor operatesimmediately, it will stop the flow of welding current between the studand plate while the stud is moving towards the plate. This circuit, thusallows welding current to flow while the plunger spring is overcomingthe inertia of the stud and :is starting to move it towards the plate.

In all of these diiferent methods and circuits the arc is initiated byrelatively low current flowing through the lifting portion of thesolenoid coil in series with the stud and plate. Closing of a contactorto initiate flow of welding current shunts the lifting coil to eliminatethis relatively small current and establish the heavy welding currentacross the are established by the small current. The are initiatingcurrent is not maintained throughout the weld cycle and is notsuperimposed on the welding current. Both the arc initiating and studlifting current and the welding current are obtained from a singlesource of current P. Thus, with this circuit only a single generator,rectifier or set of batteries is needed for the welding operation.

Although this invention has been described in its preferred form with acertain degree of particularity enabling others to reproduce theinvention, it is understood that the present disclosure has been made byway of example and that numerous modifications and changes in thedetails may be resorted to without departing from the spirit and scopeof the invention as defined in the claims which are made a part hereof.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a stud welding device, a housing, a stud carrying member,resilient means urging the stud carrying member away from the housing, asolenoid in the housing including an armature operatively connected tothe stud carrying member and a coil capable of overcoming the resilientmeans and drawing the armature and the stud carrying member towards thehousing, first means including a switch for connecting one end of .thesolenoid coil to one side of .a welding current source, a lead forconnecting the other end of the solenoid coil to the other side of awelding current source, second means including a contactor forconnecting the stud carrying member to the said one side of the weldingcurrent source and electrically connecting the stud carrying member tothe solenoid coil at a point between the ends thereof, and timing meansconnected to and controlling said switch and said contactor.

2. The structure of claim 1 wherein said timing means is operative toclose said switch prior to the closing of said contactor.

3. The structure of claim 1 wherein said timing means is operative toclose said switch prior to the closing of said contactor and isoperative to open said switch prior to the opening of said contactor.

4. The structure of claim 1 including a lead switch in said lead andcontrolled by the timing means to operate simultaneously with the switchin the first means.

5. The structure of claim 3 including a lead switch in said leadcontrolled by the timing means to operate simultaneously with the switchin the first means.

6. In a stud welding device, a housing, a stud carrying member,resilient means urging the stud carrying member away from the housing, asolenoid coil in the housing, solenoid armature means operativelyconnected to the stud carrying member, a welding current contactor, aswitch, a first circuit connecting at least a first part of saidsolenoid coil and said switch in series with said stud carrying member,a second circuit connecting at least a second part of said solenoid inparallel with said ages:

stud carrying member, saidcontactor shunting the first part of saidsolenoid, and timing means controlling said switch and said contactor.

7'. The structure of claim 6 wherein the timing means is operative toclose the switch prior to the closing of the contacto'r and is operativeto open the switch after the closing of the contactor and prior to theopening of the contactor.

8; The structure of claim 1 including a switch in said lead controlledby the timing means to close prior to the closing of the contactor andto open prior to the opening of the contactor.

9. The structure of claim 3 including a switch in said lead controlledby the timing means to close prior to the closing of the contactor andto open prior to the opening of the contactor.

105111 a stud welding device, a housing, a stud carrying, member,resilient means urging the stud carrying memher away from the housing,a; solenoid in the housing, including an armature operatively connectedto the stud carrying member and: a coil capable of overcoming theresilient means and drawing the armature and the stud: carrying: membertowards the housing, first means connecting one end of the solenoid coilto one side of a welding current source, second means connecting theother end of the solenoid coil to the other side "of a welding currentsource, third means including a cont-actor for connecting the studcarrying member to the said one side of the welding current source andelectrically connecting the stud carrying member to the solenoid coil ata point between the ends thereof, a switch in at least one of saidmeans, and timing means connected to and opening and closing said switchand said contactor in a predetermined sequence of operation.

1 1-. In a stud welding device adapted to lift a stud from awork pieceto draw an arc therebetween, a stud carrying member, a lifting coil, aholding coil, a first circuit connecting said lifting coil in serieswith said stud carrying member, a second circuit connecting said holdingcoil in parallel with said stud carrying member, and means controllingsaid first and second circuits.

12. In a stud welding device adapted to lift a stud from a work piece todraw an arc therebetween, a stud carrying member, a lifting coil, aholding coil, a first circuit including a switch connecting said liftingcoil in series with said member, a second circuit including a contactorshunting at least said lifting coil and connecting said holding coil inparallel With said stud carrying member, and control means controllingsaid switch and said contactor.

[3. In a drawn-arc welding apparatus having mechanical provisions forplacing two members into contact in rhe approximate position in whichthey are to be welded and to guide the members in a relative separationand return movement, the provision of improved electrical apparatus andcircuitry to cause the relative separation and u controlled arc weldingaction, comprising means to drive said workpieces into a contactposition, an electricul prime mover, meansresponsive tosaid prime moverwhen energized to cause said relative separation of the workpieces, asingle welding current source having first and second terminals, firstcircuit means including said electrical prime mover and said workpiecesconnectuble across said terminals in series for energizing said primemover and causing the workpieces to separate and draw a pilot arctherebetween, a second circuit between the said terminals including saidworkpieces, said workpieces being a common portion of said first andsecond circuits, a portion of said second circuit being in parallelcircuit to the portion of said first circuit which includes theelectrical prime mover, and switch control means operatively connectedto first energize said first circuit and thereby energize the primemover to separate the workpieces and thereafter energize the secondcircuit to supply nu welding current to said workpieces to shun-t theprime mover, whereby the power to the prime mover is do creasedsimultaneously and instantaneously as a function of the closing of saidsecond circuit.

14. In a drawn-arc welding apparatus having mechanical provisions forplacing two members into contact in; theapproximate position in whichthey are to be welded and to guide the members in a relative separationand return movement, the provision of improved electrical apparatus andcircuitry to cause the relative separation and a controlled arc weldingaction, comprising, means urging said workpieces into a contactposition, a solenoid prime mover, means responsive to said prime moverwhen energized to cause said relative separation of the workpiecesagainst the force of the means urging said workpieces into contactposition, a single welding current source: having first and secondterminals, first circuit means including said solenoidand saidworkpieces com nectable across said terminals in series for energizingsaid solenoid prime mover and causing the workpieces to separate anddraw a pilot arc therebetween, a second circult between the saidterminals in series with said work: pieces, said workpieces being acommon portion of said first and second circuits, a portion of saidsecond circuit being in parallel to a! portion of said first circuit,said portion of said first circuit including at least a part of saidsolenoid, said second circuit including a switch means, whereby whensaid switch means is actuated to supply full welding current to saidworkpieces the said solenoid may be at least partially shunted by thesecond circuit to reduce the power thereof, said solenoid in saidshunted condition having a magnetic power lower than required to causethe said relative separation against the means urging said workpiecestogether.

15. In a welding apparatus as defined in claim 14 said solenoid being asingle operative unit included entirely in the first circuit and beingfully shunted by said second circuit.

16. In a welding apparatus as defined in claim 14, said solenoid beingcomposed of a high ampere-turn portion and a low ampere-turn portion,said first circuit includ ing a conductor circuit from said firstterminal through a switch to said high ampere-turn portion, a conductorcircuit from said high ampere-turn portion to said stud and a circuitthrough said low ampere-tum portion and a switch to the second terminal;said second circuit including u conductor circuit from said firstterminal directly to said stud through a switch, whereby said solenoidwill be activated to lift the stud and draw an arc by closing of thesaid switch from the first terminal to the solenoid, and may thereafterbe rendered inefiectively by closing the. switch in the second circuitto shunt the said high ampere-turn portion, and whereby said stud may beheld retracted after said high-ampere-turn portion is shunted by havingthe switch closed in the circuit from said low ampere-turn portion, andmay be freed of holding restrain! by opening the last said switchregardless of the flow of current in said second circuit.

17. Ina stud welding device, a housing, a stud carrying member, asolenoid armature extending in said housing and adapted to drive saidstud carrying member, resilient means urging the armature to drive saidstud carrying member away from the housing, a solenoid coil associ atedwith said armature capable of overcoming the resilient means and drawingthe stud carrying member and a stud supported thereby toward thehousing, first circuit means including a switch connecting said solenoidcoil and said stud carrying member in series to one side of a weldingcurrent source, said first circuit means thereby being completed bycontact of a stud in the carrying device to the other side' of saidwelding current source, secand circuit means including a contactorconnecting said stud carrying member directly to said one side of thewelding current source thereby shunting said switch and said coil, andtiming means controlling said switch and con-factor to sequentiallyclose said first circuit and thereafter close said second circuit,whereby the coil draws the stud toward the housing and supplies acurrent of limited value to the stud to draw a pilot arc and whereby thesecond circuit thereafter shunts the coil to reduce the current drawnthereby and supply a full welding power direct to the stud in the studcarrying member, said shunting providing an instantaneous alteration ofthe solenoid holding power and change of welding are from pilot to fullweld power.

18. In a stud welding device, a housing, a stud carrying member,resilient means urging the stud carrying member away from the housing, asolenoid in the housing including an armature operatively connected todrive the stud carrying member, said solenoid having a coil capable ofovercoming the resilient means and drawing the armature and driving thestud carrying member toward the housing, first circuit means including aswitch operative for electrically connecting one end of the solenoidcoil to one side of a welding curent source, second circuit meansoperative for electrically connecting the stud carrying member to theother end of the solenoid coil, third circuit means including acontactor connecting said stud carrying member directly to said one sideof the welding current source, thereby shunting said switch and saidcoil, and timing means controlling said switch and said contactor tosequentially close said first circuit means and direct current throughsaid coil and said second circuit means to said stud carrying means, andthereafter close said third circuit means, whereby the solenoid drawsthe stud toward the housing and supplies a current of limited value tothe stud to draw a pilot arc and whereby the third circuit thereaftershunts the coil to reduce the current drawn thereby and supply a fullwelding power direct to the stud in the stud carrying member, saidshunting providing an instantaneous alteration of the solenoid holdingpower and change of welding arc from pilot to full weld power.

References Cited in the file of this patent or the origlnal patentUNITED STATES PATENTS 2,265,169 Hughes Dec. 9, 1941 2,342,144 HughesFeb. 22, 1944 2,462,882 Martin Mar. 1, 1949 2,467,723 Barlow Apr. 19,1949 2,648,748 Sayer Aug. 11, 1953

